1. Field of the Invention
The present invention relates to a radio communication apparatus comprising a base unit connected to at least one wired line and a plurality of mobile units connected through radio communication channels to the base unit, and more particularly to a radio communication apparatus in which each of the mobile units is able to know whether the wired line connected to the base unit is in a communication state, in a hold state or in an idle state.
2. Description of the Related Art
A radio communication apparatus of this type is generally provided and used inside the buildings, and connected to wired lines such as public telephone lines. The apparatus includes a base unit disposed at a fixed position inside a room and mobile units connected to the base unit through radio communication channels. Each mobile unit captures the wired line through the base unit and starts communication with an incoming caller or a destination party.
FIG. 15 illustrates the structure of a radio communication apparatus wherein a base unit 1 is connected through a radio communication channel to a mobile unit 2 and also to a wired telephone line 3.
In the base unit 1, a voice signal from the wired telephone line 3 is supplied as a modulating input to a transmitter 6 through a line relay 4 and a hybrid circuit 5, and the transmitter 6 transmits the modulated voice signal through a transmission antenna 7 to the mobile unit 2. The voice signal transmitted from the mobile unit 2 is received by a reception antenna 8 and demodulated by the receiver 9. The demodulated voice signal is delivered to the wired line 3 through the hybrid circuit 5 and a line relay 4 in a closed state. A synthesizer 10 generates a signal having a frequency corresponding to a control channel and one of a plurality of speech channels to the transmitter 6 and to the receiver 9. The transmitter 6 and the receiver 9 transmit and receive signals through the channel corresponding to the frequency of the signal from the synthesizer 9, respectively.
One of the outputs from the receiver 9 is input to a received field detector 11 for determining the received field strength. The detector 11 is generally referred to as a carrier squelch circuit or a noise squelch circuit.
Another output from the receiver 9 includes a data signal contained in the demodulated received waves and is input to an identification signal detector 12 which checks an identification signal determined by the combination of the host and mobile units 1 and 2. The identification signal is generally referred to as an ID code.
The output of the detector 11 and the demodulated output of the data signal are input to a control circuit 13 for connection control. The control circuit 13 performs a controlling operation such as a control of the synthesizer 10 and hence a control of radio channels, and delivery of a transmitted data signal as a modulating input to the transmitter 6.
A call signal detector 14 detects a call signal arriving from the wired telephone line 3 and informs the control circuit 13 of the arrival.
A rectifying and stabilizing circuit 15 converts an AC voltage available through an AC plug 16 into a DC voltage, which is supplied to the respective elements of the base unit 1 and applied also through a limiting resistor 17 across a pair of charging terminals 18a and 18b.
The mobile unit 2 includes a reception antenna 21 and a receiver 22. The electric waves from the base unit 1 are received by the reception antenna 21 and the resulting signal is demodulated by the receiver 22 which outputs the demodulated signal or voice signal to an ear piece 23. A voice signal from a mouth piece 24 is delivered as a modulating input to the transmitter 25 and transmitted from the transmission antenna 26. A synthesizer 27, a received field detector 28, and an identification signal detector 29 are similar to those of the base unit 1. A control circuit 30 controls the mobile unit 2. A dialing unit 31 is operated to input dialing data, etc., to the control circuit 30. A hook switch 32 is operated to select between the off-hook state and the on-hook state. A speaker 33 is a sounder which generates a ringing tone when there is an incoming call.
A secondary battery 34 supplies voltages to the required elements of the radio telephone 2. The battery 34 is charged through a current limiting resistor 17 from the rectifying and stabilizing circuit 15 of the base unit 1 when the terminals 35a and 35b are connected to the charging terminals 18a, 18b, respectively.
When there is an incoming call signal in the apparatus, control is provided substantially in accordance with the flowchart of FIG. 16. When the call signal detector 14 detects a call signal from the wired telephone line 3 when the base unit 1 is in its standby state (step 101), the synthesizer 10 is set in the control channel to turn on the transmitter 6 to thereby transmit a notice signal indicative of the reception of the call signal to the mobile unit 2 (step 102). The notice signal also includes a signal designating a speech channel S-CH.
On the other hand, the mobile unit 2 turns on the synthesizer 27 for a predetermined time t1 during its standby to set the synthesizer in the control channel and to turn on the receiver 22 (step 201). When the notice signal is received at this time (step 202), the transmitter 25 is turned on (step 203) to send a notice signal responsive signal to the base unit (step 204) to thereby select the designated speech channel S-CH (step 205). If no notice signal is received, the synthesizer 27 and the receiver 22 are turned off for a predetermined time t2 (step 206).
Intermittent reception by turning on/off the receiver is referred to as battery saving.
The average current IA consumed in the standby in the mobile unit state is given by IA=(t1.times.Ion+t2.times.Ioff)/(t1+t2) where Ioff is the current consumed when the receiver is off and Ion is the current consumed when the receiver is on. Since Ion&gt;&gt;Ioff usually, the consumed current IA is low.
When the received field detector 11 of the base unit 1 detects the electric waves from the mobile unit 2 (step 103), transmission of the notice signal is stopped (step 104). If no electric waves are detected, the notice signal is transmitted successively up to a predetermined number of (n) times (step 105). The reason why the notice signal is successively transmitted so is that the mobile unit 2 cannot receive the notice signal for t2 because of its intermittent reception. Thus, the notice signal transmitted is required to be two signal wavelengths longer than t2. The reason why the transmission of the notice signal more than n times is stopped is to avoid unnecessarily long occupation of the control channel when the mobile unit 2 is not powered up or is located at an excessively distant place.
The base unit 1 determines whether the ID code contained in the notice signal responsive signal received when the received field is detected coincides with a registered one or not. If so, (step 106), the speech channel S-CH designated by the notice signal is selected (step 107). If the ID code does not coincide, the notice signal responsive signal may be from another radio communication device, so that the standby state of the base unit is restored when the calling signal from the wired telephone line 3 has disappeared (step 108).
After the speech channel S-CH is selected, the base unit 1 sends a bell ringing signal (step 109). When the mobile unit 2 receives it (step 207), the speaker 33 generates a calling tone (step 208). If the off-hook switch goes off-hook at this time (step 209), an off-hook signal is sent to the base unit (step 210) to thereby result in a telephone communication state (step 211).
When the base unit 1 receives the off-hook signal (step 110), it stops the transmission of the bell ringing signal (step 111), and closes the line relay 4 to form a speech loop with the wired telephone line 3 to bring about a telephone communication state (step 112).
When the frequency of transmitting the notice signal arrives at n, the base unit 1 returns to its standby state after it detects the end of the notice signal (step 113) to thereby prevent unnecessary signal receiving operation from being performed again.
Control of call origination is provided substantially in accordance with the flowchart of FIG. 17. When the hook switch 32 is switched on to bring about the off-hook state in the mobile unit 2, call origination starts (step 301) to set the synthesizer 27 in the control channel C-CH and to turn on the receiver 22 (step 302). At this time, the received field detector 28 checks whether the control channel is idle (step 303) and, if so, turns on the transmitter 25 to thereby cause same to send a call origination signal (step 304). The call origination signal includes an ID code.
The base unit 1 sets the synthesizer 10 in the control channel when the base unit is in its standby state to maintain the receiver 9 on. When the receiver 9 receives a call origination signal (401), it determines whether the ID code contained in the call origination signal coincides with the registered one or not (step 402). If the ID code coincides, the transmitter 6 is turned on to send a responsive signal to the mobile unit (step 403). The responsive signal includes an ID code and a signal designating a speech channel S-CH. Thereafter, the synthesizer 10 is changed from the control channel C-CH to the speech channel S-CH designated by the responsive signal (step 404) to thereby close the line relay 4 to bring about a telephone communication state.
The mobile unit 2 continues to detect electric waves from the base unit 1 using the received field detector 28 until a time t has passed (steps 305, 306). If the detector 28 detects a received field when the responsive signal is received, it checks whether the ID code contained in the responsive signal coincides with the registered one. If so (step 307), it switches the synthesizer 27 to the speech channel designated by the responsive signal (step 308) to thereby bring about a telephone communication state. If the ID code does not coincide, the responsive signal may be from another radio communication device, so that the mobile unit returns to its standby state. If no electric waves from the base unit 1 are detected even if a time t has passed, the speaker 33 generates an alarm sound indicating that connection is impossible because the host and mobile units 1 and 2 are, for example, excessively distant from each other (step 309), and the mobile unit returns its standby state.
FIG. 18 illustrates a modification of the radio communication apparatus as mentioned above. In FIG. 18, the base unit 51 has a plurality of wired lines 52-l to 52-m connected thereto and a plurality of mobile units 53-l to 53-n connected thereto through radio communication channels. In this case, the mobile unit 53-l to 53-n share the wired lines 52-l to 52-m through the base unit 51. An ID code is allocated to each of the combinations of the mobile units 53-l to 53-n with the base unit 51, so that the call reception and origination shown with reference to FIGS. 16 and 17 are possible with the respective mobile units.
Since the mobile units share the plurality of wired lines, they can use the radio communication apparatus more efficiently if they can know whether the respective wired lines are in use. For example, if (1) pieces of information on busy lines, held lines and idle lines are displayed in the mobile units, (2) the base unit is informed by the mobile units of the desired wired lines in accordance with the displayed pieces of information and (3) the mobile units are connected to the corresponding desired wired lines through the base unit, the radio communication apparatus will be used more efficiently.
However, as mentioned above, when a mobile unit is in its standby state, its transmitter is off and the mobile unit is placed in an intermittent reception state for battery saving purposes. Thus, information cannot be exchanged when required between the standby state mobile unit and the base unit. Therefore, the mobile units require some new improvements thereon in order to know the status of the wired lines.